{
  "bibcode": "2024GCN.37149....1S",
  "circularId": 37149,
  "submitter": "Phil Evans at U of Leicester <pae9@star.le.ac.uk>",
  "body": "T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini\n(INAF-OAB), J. D. Gropp (PSU), S. Dichiara (PSU), J.A. Kennea (PSU),\nJ.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and P.A. Evans\nreport on behalf of the Swift-XRT team:\n\nWe have analysed 6.7 ks of XRT data for GRB 240811A, from 84 s to 39.6\nks after the  BAT trigger. The data comprise 41 s in Windowed Timing\n(WT) mode (the first 9 s were taken while Swift was slewing) with the\nremainder in Photon Counting (PC) mode. \n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=4.2 (+/-0.3), followed by a break at T+240 s to an alpha\nof 0.42 (+/-0.04).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.97 (+0.19, -0.17). The\nbest-fitting absorption column is  5.1 (+4.6, -3.1) x 10^20 cm^-2,\nconsistent with the Galactic value of 2.0 x 10^20 cm^-2 (Willingale et\nal. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 3.4 x 10^-11 (3.8 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     5.1 (+4.6, -3.1) x 10^20 cm^-2\nGalactic foreground: 2.0 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.97 (+0.19, -0.17)\n\nIf the light curve continues to decay with a power-law decay index of\n0.42, the count rate at T+24 hours will be 0.036 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x\n10^-12 (1.4 x 10^-12) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01248132.\n\nThis circular is an official product of the Swift-XRT team.\n",
  "subject": "GRB 240811A: Swift-XRT refined Analysis",
  "submittedHow": "email",
  "createdOn": 1723460746949,
  "eventId": "GRB 240811A"
}